Curable silicone resin composition

ABSTRACT

A curable silicone resin composition is provided which is useful as a material for optical devices or parts, insulation material for electronic devices or parts, or coating material, and which produces a cured product having high hardness and strength and further having good optical transmission in the short wavelength region. The composition includes (A) an aromatic hydrocarbon compound having at least two hydrogen atoms bonded to silicon atoms with the silicon atoms being bonded to the hydrocarbon skeleton of the aromatic hydrocarbon compound, (B) a cyclic siloxane compound having at least two silicon atom-bonded alkenyl groups, and (C) a hydrosilylation reaction catalyst, or (D) an aromatic hydrocarbon compound having at least two alkenyl groups bonded to silicon atoms with the silicon atoms being bonded to the hydrocarbon skeleton of the aromatic hydrocarbon compound, (E) a cyclic siloxane compound having at least two silicon atom-bonded hydrogen atoms, and (C) a hydrosilylation reaction catalyst.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a curable silicone resincomposition which is useful as a material for optical devices or parts,insulation material for electronic devices or parts, or coatingmaterial.

[0003] 2. Description of the Prior Art

[0004] Conventionally, epoxy resins have been generally used as amaterial for optical devices or parts, in particular, sealing materialfor light emitting diode (LED) elements. In addition, it has beenattempted to use a silicone resin as a molding material for LED elements(see Patent Documents 1 and 2) and also to use it as a color filtermaterial (see Patent Document 3). However, examples of practicalapplications are few.

[0005] Recently, under circumstances where white LEDs are paid attentionto, problems, which were not subjects of discussion before, such asyellowing of an epoxy sealing material caused by ultraviolet rays orcracking caused by increase of heat generation associated withdownsizing of the white LEDs have occurred and solution is soughturgently. To address these problems, use of a cured product of asilicone resin with a number of phenyl groups is examined. Meanwhile,LED light sources which emit light with a shorter wavelength tend to beused presently. However, since epoxy sealing materials and phenylgroup-containing silicone resin sealing materials have poor opticaltransmission in the short wavelength region, they are unsuitable to beapplied to LEDs which emit light in the short wavelength region.

[0006] Patent Document 1: Japanese Laid-open Patent publication (kokai)No. Hei 10-228249 (JP10-228249A)

[0007] Patent Document 2: Japanese Laid-open Patent publication (kokai)No. Hei 10-242513 (JP10-242513A)

[0008] Patent Document 3: Japanese Laid-open Patent publication (kokai)No. 2000-123981 (JP2000-123981A)

SUMMARY OF THE INVENTION

[0009] The present invention has been made in consideration of theaforementioned circumstances and has an object to provide a curablesilicone resin composition which is useful as a material for opticaldevices or parts, insulation material for electronic devices or parts,or coating material, and which produces a cured product having highhardness and strength and further having good optical transmission inthe short wavelength region.

[0010] The present inventors made extensive efforts to achieve thisobject. As a result, the present inventors have discovered that asilicone resin composition comprising an aromatic hydrocarbon compoundhaving hydrogen atoms or alkenyl groups bonded to silicon atoms withsaid silicon atoms being bonded to the hydrocarbon skeleton of saidaromatic hydrocarbon compound, and a cyclic siloxane compound havingsilicon atom-bonded alkenyl groups or hydrogen atoms in combinationgives, on curing with hydrosilylation reaction, a cured product havingthe aforementioned properties. Based on this discovery, the presentinventors have completed the present invention.

[0011] Thus, as the first aspect, the present invention provides acurable silicone resin composition comprising:

[0012] (A) an aromatic hydrocarbon compound having at least two hydrogenatoms bonded to silicon atoms, said silicon atoms being bonded to thehydrocarbon skeleton of said aromatic hydrocarbon compound;

[0013] (B) a cyclic siloxane compound having at least two siliconatom-bonded alkenyl groups; and

[0014] (C) a hydrosilylation reaction catalyst (hereinafter referred toas “first invention”).

[0015] As the second aspect, the present invention provides a curablesilicone resin composition comprising:

[0016] (D) an aromatic hydrocarbon compound having at least two alkenylgroups bonded to silicon atoms, said silicon atoms being bonded to thehydrocarbon skeleton of said aromatic hydrocarbon compound;

[0017] (E) a cyclic siloxane compound having at least two siliconatom-bonded hydrogen atoms; and

[0018] (C) a hydrosilylation reaction catalyst (hereinafter referred toas “second invention”).

[0019] Hereinafter, silicon atom-bonded hydrogen atoms are sometimesreferred to as “SiH groups”.

[0020] In the second invention, —CH═CH₂ groups in the alkenyl groupsbonded to silicon atoms contained in the aromatic hydrocarbon compoundundergo hydrosilylation addition reaction, well-known to a personskilled in the art, with SiH groups contained in the cyclic siloxanecompound. In the first invention, SiH groups contained in the aromatichydrocarbon compound undergo hydrosilylation addition reaction with—CH═CH₂ groups in the alkenyl groups bonded to silicon atoms containedin the cyclic siloxane compound. Both inventions are equivalent in thatthey form the same linkage structure to provide cured products.

[0021] The curable silicone resin composition of the present inventioncan provide a cured product having high hardness and strength, goodoptical transmission rate for light in the short wavelength region, andexcellent transparency. Therefore, the composition can preferably beused, for example, for protection, sealing, or adhesion of LED elements,change or adjustment of wavelength of LED elements, or lenses of LEDelements. The composition can also be used as various optical materialssuch as a lens material, sealing material for optical devices or parts,or display material, insulation material for electronic devices orparts, and coating material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will now be described below in detail.

First Invention

[0023] [(A) Aromatic Hydrocarbon Compound]

[0024] The component (A) is an aromatic hydrocarbon compound having atleast two SiH groups, said silicon atoms being bonded to the hydrocarbonskeleton of said aromatic hydrocarbon compound.

[0025] Preferably, the component (A) is, for example, a compoundrepresented by the general formula (1):

HR¹R²Si-A-SiR³R⁴H  (1)

[0026] wherein R¹, R², R³, and R⁴ each independently represent ahydrogen atom or a group selected from the group consisting of anunsubstituted monovalent hydrocarbon group having 1 to 12 carbon atomsand preferably 1 to 6 carbon atoms except an alkenyl group, asubstituted monovalent hydrocarbon group having 1 to 12 carbon atoms andpreferably 1 to 6 carbon atoms except an alkenyl group, and an alkoxygroup having 1 to 6 carbon atoms and preferably 1 to 4 carbon atoms; andA represents an aromatic ring-containing divalent hydrocarbon grouphaving 6 to 12 carbon atoms and preferably 6 to 10 carbon atoms.

[0027] When the R¹ to R⁴ are monovalent hydrocarbon groups exceptalkenyl groups, examples thereof include alkyl groups such as methylgroups, ethyl groups, propyl groups, isopropyl groups, butyl groups,tert-butyl groups, pentyl groups, isopentyl groups, hexyl groups, andsec-hexyl groups; aryl groups such as phenyl groups and o-, m-, orp-tolyl groups; aralkyl groups such as benzyl groups and 2-phenylethylgroups; and groups in which at least one hydrogen atom of these groupshave been substituted with halogen atoms, cyano groups, epoxygroup-containing groups, or the like, for example, halogenated alkylgroups such as chloromethyl groups, 3-chloropropyl groups, and3,3,3-trifluoropropyl groups, 2-cyanoethyl groups, and 3-glycidoxypropylgroups.

[0028] When the R¹ to R⁴ are alkoxy groups, examples thereof includemethoxy groups, ethoxy groups, propoxy groups, isopropoxy groups, butoxygroups, sec-butoxy groups, and tert-butoxy groups.

[0029] Of compounds represented by the general formula (1), those inwhich all of the R¹ to R⁴are methyl groups are preferred because theyare easy to industrially produce and are easily available.

[0030] Examples of aromatic ring-containing hydrocarbon groupsrepresented by the A include o-, m-, or p-phenylene groups, tolylenegroups, o-, m-, or p-xylylene groups, and divalent arylene groupsrepresented by the formulas:

[0031] Preferred specific examples of the component (A) are shown blowbut are not limited thereto. Hereinafter, “Me” stands for a methylgroup, “Et” stands for an ethyl group, “Ph” stands for a phenyl group,“-p-C₆H₄—” stands for a para-phenylene group, and “-m-C₆H₄—” stands fora meta-phenylene group.

[0032] HMe₂Si-p-C₆H₄—SiMe₂H

[0033] HMe₂Si-m-C₆H₄—SiMe₂H

[0034] HMePhSi-p-C₆H₄—SiMePhH

[0035] HMePhSi-m-C₆H₄—SiMePhH

[0036] HPh₂Si-p-C₆H₄—SiPh₂H

[0037] HPh₂Si-m-C₆H₄—SiPh₂H

[0038] HMeEtSi-p-C₆H₄—SiMeEtH

[0039] HMeEtSi-m-C₆H₄—SiMeEtH

[0040] H(MeO)₂Si-p-C₆H₄—Si(OMe)₂H

[0041] H(MeO)₂Si-m-C₆H₄—Si(OMe)₂H

[0042] HMe₂Si—CH₂-p-C₆H₄—CH₂—SiMe₂H

[0043] HMe₂Si—CH₂-m-C₆H₄—CH₂—SiMe₂H

[0044] HMePhSi—CH₂-p-C₆H₄—CH₂—SiMePhH

[0045] HMePhSi—CH₂-m-C₆H₄—CH₂—SiMePhH

[0046] These may be used singularly, or in combination of two or more.

[0047] [(B) Cyclic Siloxane Compound]

[0048] The component (B) is a cyclic siloxane compound having at leasttwo silicon atom-bonded alkenyl groups and capable of undergoinghydrosilylation addition reaction with the component (A).

[0049] Preferably, the component (B) is, for example, a cyclic siloxanecompound represented by the general formula (2):

(R^(a)R⁵SiO)_(n)(R⁶R⁷SiO)_(m)  (2)

[0050] wherein R^(a) represents an alkenyl group having 2 to 6 carbonatoms and preferably 2 to 3 carbon atoms, R⁵, R⁶, and R⁷ eachindependently represent an unsubstituted or substituted monovalenthydrocarbon group having 1 to 12 carbon atoms and preferably 1 to 6carbon atoms, n represents an integer from 2 to 10, and m represents aninteger from 0 to 8, provided that n+m represents an integer from 3 to10 and preferably from 3 to 6.

[0051] Examples of the R^(a) include vinyl groups, allyl groups,propenyl groups, isopropenyl groups, butenyl groups, pentenyl groups,and hexenyl groups. Of these, vinyl groups and allyl groups arepreferred, and vinyl groups are particularly preferred.

[0052] Examples of the R⁵ to R⁷ include the alkenyl groups exemplifiedfor the R^(a) and the monovalent hydrocarbon groups exemplified for theR¹ to R⁴.

[0053] Preferred specific examples of the component (B) are shown blowbut are not limited thereto. Hereinafter, “Vi” stands for a vinyl group,“Allyl” stands for an allyl group, and “Pr” stands for an n-propylgroup.

[0054] (ViMeSiO)₃

[0055] (ViMeSiO)₄

[0056] (AllylMeSiO)₃

[0057] (AllylMeSiO)₄

[0058] (ViMeSiO)₂(Me₂SiO)₂

[0059] (ViMeSiO)₃(Me₂SiO)₁

[0060] (ViMeSiO)₂(PrMeSiO)₂

[0061] (ViMeSiO)₃(PrMeSiO)₁

[0062] These may be used singularly, or in combination of two or more.

[0063] The components (A) and (B) are present in the composition of thefirst invention such that the quantity of the SiH groups in thecomponent (A) is preferably 0.5 to 2.0 mol and more preferably 0.8 to1.5 mol per mol of the alkenyl groups in the whole composition. Theproportion of the alkenyl groups in the component (B) to the alkenylgroups in the whole composition is preferably 10 mol % or more andparticularly preferably 30 mol % or more. In the case where only thecomponent (B) is present in the composition as a component havingalkenyl groups, the components (A) and (B) are present in thecomposition such that the quantity of the SiH groups in the component(A) is preferably 0.5 to 2.0 mol and more preferably 0.8 to 1.5 mol permol of the alkenyl groups in the component (B).

[0064] [(C) Hydrosilylation Reaction Catalyst]

[0065] All the hydrosilylation reaction catalysts conventionally knowncan be used as the component (C). Specific examples thereof includeplatinum-based catalysts such as platinum black, platinic chloride,chloroplatinic acid, a reaction product of chloroplatinic acid and amonohydric alcohol, a complex of chloroplatinic acid and olefins, andplatinum bis(acetoacetate); and platinum group metal-based catalystssuch as palladium-based catalysts and rhodium-based catalysts.

[0066] Preferably, the quantity of the component (C) is an effectivequantity as catalyst. More preferably, a typical quantity, calculated asthe weight of the platinum group metal atom within the catalyst relativeto the combined weight of the components (A) and (B), is within a rangefrom 1 to 500 ppm and particularly from 2 to 100 ppm.

Second Invention

[0067] [(D) Aromatic Hydrocarbon Compound]

[0068] The component (D) is an aromatic hydrocarbon compound having atleast two alkenyl groups bonded to silicon atoms, said silicon atomsbeing bonded to the hydrocarbon skeleton of said aromatic hydrocarboncompound.

[0069] Preferably, the component (D) is, for example, an aromatichydrocarbon compound represented by the general formula (3):

R^(a)R⁸R⁹Si-A-SiR¹⁰R¹¹R^(b)  (3)

[0070] wherein R^(a) and R^(b) each independently represent an alkenylgroup having 2 to 6 carbon atoms and preferably 2 to 3 carbon atoms; R⁸,R⁹, R¹⁰, and R¹¹ each independently represent a group selected from thegroup consisting of an unsubstituted monovalent hydrocarbon group having1 to 12 carbon atoms and preferably 1 to 6 carbon atoms, a substitutedmonovalent hydrocarbon group having 1 to 12 carbon atoms and preferably1 to 6 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms andpreferably 1 to 4 carbon atoms; and A is as defined for the formula (1).

[0071] Examples of the R^(a) and R^(b) include the groups exemplifiedfor the R^(a) as defined for the formula (2). Examples of the R⁸ to R¹¹include the groups exemplified for the R^(a) as defined for the formula(2) and the groups exemplified for the R¹ to R⁴ as defined for theformula (1) except a hydrogen atom.

[0072] Preferred specific examples of the component (D) are shown blowbut are not limited thereto.

[0073] ViMe₂Si-p-C₆H₄—SiMe₂Vi

[0074] ViMe₂Si-m-C₆H₄—SiMe₂Vi

[0075] ViMePhSi-p-C₆H₄—SiMePhVi

[0076] ViMePhSi-m-C₆H₄—SiMePhVi

[0077] ViMe₂Si—CH₂-p-C₆H₄—CH₂—SiMe₂Vi

[0078] ViMe₂Si—CH₂-m-C₆H₄—CH₂—SiMe₂Vi

[0079] ViMePhSi—CH₂-p-C₆H₄—CH₂—SiMePhVi

[0080] ViMePhSi—CH₂-m-C₆H₄—CH₂—SiMePhVi

[0081] ViMe(MeO)—CH₂-p-C₆H₄—CH₂—Si(OMe)MeVi

[0082] ViMe(MeO)—CH₂-m-C₆H₄—CH₂—Si(OMe)MeVi

[0083] ViMe(EtO)—CH₂-p-C₆H₄—CH₂—Si(OEt)MeVi

[0084] ViMe(EtO)—CH₂-m-C₆H₄—CH₂—Si(OEt)MeVi

[0085] These may be used singularly, or in combination of two or more.

[0086] [(E) Cyclic Siloxane Compound]

[0087] The component (E) is a cyclic siloxane compound having at leasttwo SiH groups and capable of undergoing hydrosilylation additionreaction with the component (D).

[0088] Preferably, the component (E) is, for example, a cyclic siloxanecompound represented by the general formula (4):

(HR¹²SiO)_(n)(R¹³R¹⁴SiO)_(m)  (4)

[0089] wherein R¹², R¹³, and R¹⁴ each independently represent a hydrogenatom or an unsubstituted or substituted monovalent hydrocarbon grouphaving 1 to 12 carbon atoms and preferably 1 to 6 carbon atoms except analkenyl group, n represents an integer from 2 to 10, and m represents aninteger from 0 to 8, provided that n+m represents an integer from 3 to10 and preferably from 3 to 6.

[0090] Examples of the R¹² to R¹⁴ include the groups exemplified for theR¹ to R⁴ as defined for the formula (1) except an alkoxy group.

[0091] Preferred specific examples of the component (E) are shown blowbut are not limited thereto.

[0092] (HMeSiO)₃

[0093] (HMeSiO)₄

[0094] (HMeSiO)₂(Me₂SiO)₁

[0095] (HMeSiO)₃(Me₂SiO)₁

[0096] (HMeSiO)₄(Me₂SiO)₁

[0097] These may be used singularly, or in combination of two or more.

[0098] The components (D) and (E) are present in the composition of thesecond invention such that the quantity of the SiH groups in the wholecomposition is preferably 0.5 to 2.0 mol and more preferably 0.8 to 1.5mol per mol of the alkenyl groups in the component (D). The proportionof the SiH groups in the component (E) to the SiH groups in the wholecomposition is preferably 10 mol % or more and particularly preferably30 mol % or more. In the case where only the component (E) is present inthe composition as a component having SiH groups, the components (D) and(E) are present in the composition such that the quantity of the SiHgroups in the component (E) is preferably 0.5 to 2.0 mol and morepreferably 0.8 to 1.5 mol per mol of the alkenyl groups in the component(D).

[0099] [(C) Hydrosilylation Reaction Catalyst]

[0100] Examples of the hydrosilylation reaction catalyst of thecomponent (C) include those as shown above. A preferred quantity of thecomponent (C) relative to the combined weight of the components (D) and(E) is also as shown above.

Other Components

[0101] In addition to the components (A) to (E), other components may beadded to the composition of the present invention as long as the effectsof the present invention do not deteriorate.

[0102] For example, to adjust the viscosity of a composition or thehardness of a cured product, a straight-chain diorganopolysiloxane ornetwork organopolysiloxane having silicon atom-bonded alkenyl groups orSiH groups, or a non-reactive straight-chain or cyclicdiorganopolysiloxane may be added.

[0103] In particular, a network organopolysiloxane composed ofmonofunctional structural units having silicon atom-bonded alkenylgroups or SiH groups and tetrafunctional structural units (SiO₂) maypreferably be added because it enables the production of a cured producthaving high transparency and good weatherability.

[0104] In the first invention, if (F1) a network organopolysiloxanehaving silicon atom-bonded alkenyl groups is added, it is present suchthat the quantity of the SiH groups in the component (A) is preferably0.5 to 2.0 mol and more preferably 0.8 to 1.5 mol per mol of the alkenylgroups in the sum of the components (F1) and (B). If (F2) a networkorganopolysiloxane having SiH groups is added, it is present such thatthe quantity of the SiH groups in the sum of the components (F2) and (A)is preferably 0.5 to 2.0 mol and more preferably 0.8 to 1.5 mol per molof the alkenyl groups in the component (B).

[0105] In the second invention, if (F1) a network organopolysiloxanehaving silicon atom-bonded alkenyl groups is added, it is present suchthat the quantity of the SiH groups in the component (E) is preferably0.5 to 2.0 mol and more preferably 0.8 to 1.5 mol per mol of the alkenylgroups in the sum of the components (F1) and (D). If (F2) a networkorganopolysiloxane having SiH groups is added, it is present such thatthe quantity of the SiH groups in the sum of the components (F2) and (E)is preferably 0.5 to 2.0 mol and more preferably 0.8 to 1.5 mol per molof the alkenyl groups in the component (D).

[0106] To ensure a required pot life, reaction retarding agents such as1-ethynylcyclohexanol and 3,5-dimethyl-1-hexyn-3-ol may be added.Furthermore, to increase the strength of cured products, inorganicfillers such as fumed silica may be added as long as the transparency isnot affected. Dyes, pigments, and flame retardants may be added asnecessary.

[0107] Conditions for curing the composition of the present inventiondepend on the quantity of the composition and are not particularlyrestricted. Normally, the composition is preferably cured at 60 to 180°C. for 5 to 180 minutes.

[0108] The composition of the present invention can be cured by applyingit to a given substrate according to the purpose and then heating theapplied composition under the aforementioned conditions.

EXAMPLES

[0109] As follows is a more specific description of the presentinvention, which presents a series of Examples and Comparative Examples,although the present invention is not restricted to the Examples.

Example 1

[0110] 53 parts by weight of (A) HMe₂Si-p-C₆H₄—SiMe₂H, 47 parts byweight of (B) (ViMeSiO)₄ (SiH in (A)/Vi in (B) (molar ratio)=1.0), and0.03 parts by weight of 1-ethynylcyclohexanol were mixed uniformly. Tothe mixture obtained, (C) a platinum-vinylsiloxane complex was added ina quantity of 20 ppm calculated as the weight of the platinum atomwithin the component (C) relative to the combined weight of thecomponents (A) and (B). The resulting solution was mixed uniformly toproduce a composition. The composition was poured into a mold assembledfrom glass plates so as to be 4 mm thick and heated at 150° C. for 2hours to produce a cured product.

Example 2

[0111] A composition was prepared and a cured product was obtained inthe same manner as Example 1, with the exception of using 67 parts byweight of (D) ViMe₂Si-p-C₆H₄—SiMe₂Vi and 33 parts by weight of (E)(HMeSiO)₄ (SiH in (E)/Vi in (D) (molar ratio)=1.0) instead of thecomponents (A) and (B) in Example 1.

Example 3

[0112] A composition was prepared and a cured product was obtained inthe same manner as Example 1, with the exception of using 23 parts byweight of (A) HMe₂Si-p-C₆H₄—SiMe₂H, 17 parts by weight of (B)(ViMeSiO)₄, and 60 parts by weight of (F1) a silicone resin with thenumber average molecular weight of 3,600 represented by the compositionformula

[0113] (ViMe₂SiO_(1/2))₃(Me₃SiO_(1/2))₁₈(SiO₂)₂₅ (SiH in (A)/Vi in (B)and (F1) (molar ratio)=1.0) instead of the components (A) and (B) inExample 1.

Example 4

[0114] A composition was prepared and a cured product was obtained inthe same manner as Example 1, with the exception of using 33 parts byweight of (A) ViMe₂Si-p-C₆H₄—SiMe₂Vi, 7 parts by weight of (B)(HMeSiO)₄, and 60 parts by weight of (F2) a silicone resin with thenumber average molecular weight of 2,300 represented by the compositionformula:

[0115] (HMe₂SiO/_(1/2))₅(Me₃SiO/_(1/2))₁₅(SiO₂)₁₀ (SiH in (E) and(F2)/Vi in (D) (molar ratio)=1.0) instead of the components (A) and (B)in Example 1.

Comparative Example 1

[0116] 41 parts by weight of (HMeSiO)₄, 59 parts by weight of(ViMeSiO)₄, and 0.03 parts by weight of 1-ethynylcyclohexanol were mixeduniformly. To the obtained mixture, a platinum-vinylsiloxane complex wasadded in a quantity of 20 ppm calculated as the weight of the platinumatom within the complex relative to the combined weight of the cyclicsiloxanes. The resulting solution was mixed uniformly to produce acomposition. A cured product was obtained from the composition in thesame manner as Example 1.

Comparative Example 2

[0117] A bisphenol A-type epoxy resin (brand name: Pelnox ME-540,manufactured by Pelnox Corporation) was poured into a mold assembledfrom glass plates so as to be 4 mm thick in the same manner as Example 1and heated at 150° C. for 8 hours to produce a cured product.

Comparative Example 3

[0118] A curable phenylsilicone resin composition (brand name:X-34-1195, manufactured by Shin-Etsu Chemical Co., Ltd., phenyl groupcontent: about 50 mol %) was poured into a mold assembled from glassplates so as to be 4 mm thick in the same manner as Example 1 and heatedat 150° C. for 8 hours to produce a cured product.

Methods for Evaluating Properties

[0119] Properties of the cured product obtained in each of the Examplesand Comparative Examples was evaluated according to the followingmethods.

[0120] Appearance

[0121] The appearance of each cured product was observed, and theresults are given in Table 1.

[0122] Hardness

[0123] According to ASTM D 2240, the hardness (Shore D) of each curedproduct was measured. The results are given in Table 1.

[0124] Elasticity Modulus

[0125] A 10 mm×100 mm specimen was prepared from each cured product witha thickness of 4 mm. The specimen was measured for elasticity modulus(MPa) was measured by a three-point bending test according to JISK-66911. The results are given in Table 1.

[0126] Optical Transmission Rate

[0127] Using a spectrophotometer, the optical transmission rate of eachcured product was measured at four wavelengths: 800, 600, and 400 nm,and 350 nm (ultraviolet region). The results are given in Table 2. TABLE1 Examples Comparative Examples Item 1 2 3 4 1 2 3 Appearance Color-Color- Color- Color- Color- Color- Color less, less, less, less, less,less, less, trans- trans- trans- trans- trans- trans- trans- parentparent parent parent parent parent parent Hardness 65 67 69 68 0 63 64(Shore D) Elasticity 1990 1900 1790 1690 0 1550 1520 Modulus (MPa)

[0128] TABLE 2 Wavelength Examples Comparative Examples (nm) 1 2 3 4 1 23 800 95% 95% 95% 95% 94% 96% 95% 600 95% 95% 95% 95% 94% 97% 95% 40094% 94% 95% 95% 94% 92% 92% 350 88% 88% 89% 89% 89% 76% 84%

[0129] [Evaluation]

[0130] The cured product of Comparative Example 1 was so soft that itshardness and so on could not be measured. Compared with the curedproducts of Comparative Examples 2 and 3, the cured product of anyExample has excellent hardness and elasticity modulus and also has anexcellent optical transmission rate, in particular, at a shortwavelength of 350 nm (ultraviolet region).

What is claimed is:
 1. A curable silicone resin composition comprising:(A) an aromatic hydrocarbon compound having at least two hydrogen atomsbonded to silicon atoms, said silicon atoms being bonded to thehydrocarbon skeleton of said aromatic hydrocarbon compound; (B) a cyclicsiloxane compound having at least two silicon atom-bonded alkenylgroups; and (C) a hydrosilylation reaction catalyst.
 2. The compositionaccording to claim 1, wherein said component (A) is an aromatichydrocarbon compound represented by the general formula (1):HR¹R²Si-A-SiR³R⁴H  (1)wherein R¹, R², R^(3 , and R) ⁴ each independentlyrepresent a hydrogen atom or a group selected from the group consistingof an unsubstituted monovalent hydrocarbon group having 1 to 12 carbonatoms except an alkenyl group, a substituted monovalent hydrocarbongroup having 1 to 12 carbon atoms except an alkenyl group, and an alkoxygroup having 1 to 6 carbon atoms; and A represents an aromaticring-containing divalent hydrocarbon group having 6 to 12 carbon atoms.3. The composition according to claim 2, wherein said A represents anaromatic ring-containing divalent hydrocarbon group having 6 to 10carbon atoms.
 4. The composition according to claim 1, wherein saidcomponent (B) is a cyclic siloxane compound represented by the generalformula (2): (R^(a)R⁵SiO)_(n)(R⁶R⁷SiO)_(m)  (2)wherein R^(a) representsan alkenyl group having 2 to 6 carbon atoms, R⁵, R⁶, and R⁷ eachindependently represent an unsubstituted or substituted monovalenthydrocarbon group having 1 to 12 carbon atoms, n represents an integerfrom 2 to 10, and m represents an integer from 0 to 8, provided that n+mrepresents an integer from 3 to
 10. 5. The composition according toclaim 4, wherein said R^(a) represents an alkenyl group having 2 or 3carbon atoms.
 6. A curable silicone resin composition comprising: (D) anaromatic hydrocarbon compound having at least two alkenyl groups bondedto silicon atoms, said silicon atoms being bonded to the hydrocarbonskeleton of said aromatic hydrocarbon compound; (E) a cyclic siloxanecompound having at least two silicon atom-bonded hydrogen atoms; and (C)a hydrosilylation reaction catalyst.
 7. The composition according toclaim 6, wherein said component (D) is an aromatic hydrocarbon compoundrepresented by the general formula (3):R^(a)R⁸R⁹Si-A-SiR¹⁰R¹¹R^(b)  (3)wherein R^(a) and R^(b) eachindependently represent an alkenyl group having 2 to 6 carbon atoms; R⁸,R⁹, R¹⁰, and R¹¹ each independently represent a group selected from thegroup consisting of an unsubstituted monovalent hydrocarbon group having1 to 12 carbon atoms, a substituted monovalent hydrocarbon group having1 to 12 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms;and A represents an aromatic ring-containing divalent hydrocarbon grouphaving 6 to 12 carbon atoms.
 8. The composition according to claim 7,wherein said R^(a) and R^(b) each independently represent an alkenylgroup having 2 or 3 carbon atoms.
 9. The composition according to claim7, wherein said A represents an aromatic ring-containing divalenthydrocarbon group having 6 to 10 carbon atoms.
 10. The compositionaccording to claim 6, wherein said component (E) is a cyclic siloxanecompound represented by the general formula (4):(HR¹²SiO)_(n)(R¹³R¹⁴SiO)_(m)  (4)wherein R¹², R¹³, and R¹⁴ eachindependently represent a hydrogen atom or an unsubstituted orsubstituted monovalent hydrocarbon group having 1 to 12 carbon atomsexcept an alkenyl group, n represents an integer from 2 to 10, and mrepresents an integer from 0 to 8, provided that n+m represents aninteger from 3 to
 10. 11. The composition according to claim 1, furthercomprising (F1) a network organopolysiloxane having silicon atom-bondedalkenyl groups.
 12. The composition according to claim 6, furthercomprising (F1) a network organopolysiloxane having silicon atom-bondedalkenyl groups.
 13. The composition according to claim 1, furthercomprising (F2) a network organopolysiloxane having silicon atom-bondedhydrogen atoms.
 14. The composition according to claim 6, furthercomprising (F2) a network organopolysiloxane having silicon atom-bondedhydrogen atoms.
 15. The composition according to claim 1, wherein saidcomponents (A) and (B) are present such that the quantity of the siliconatom-bonded hydrogen atoms in said component (A) is 0.5 to 2.0 mol permol of the alkenyl groups in said component (B), and said component (C)is present in an effective quantity as catalyst.
 16. The compositionaccording to claim 6, wherein said components (D) and (E) are presentsuch that the quantity of the silicon atom-bonded hydrogen atoms in saidcomponent (E) is 0.5 to 2.0 mol per mol of the alkenyl groups in saidcomponent (D), and said component (C) is present in an effectivequantity as catalyst.
 17. A cured product obtained by curing thecomposition according to claim
 1. 18. A cured product obtained by curingthe composition according to claim 6.